We chose Oceania to try a different cruise line. Spent a lot of time on Cruse Critic forums to get some idea of what to expect.
The ship is outstanding, as is the service from the crew. So attentive that it could have become annoying. Sometimes you just like to sit....quietly :)
The cabin, we had a Penthouse Suite was very nice. It was as large as most cabins we have had with Celebrity. The sq footage seems bigger but, there is a bathtub. Removal of the (unused) tub would have allowed quite a bit of extra room in the cabin. The cabin attendants were perfect. Always there when we needed them. The Butler, in our opinion, was not up to par (?) and overall, just necessary. The attendants did more and took much better care of us. We tried twice and he did not answer the phone when we called and then asked us to give him a very good rating in our mid cruise evaluation. I asked him why we would rate him as we did not see him and did not answer and he got quite, well, not pleasant.
Typical cabin, bathtub took up room and the actual cabin is not so big, typical of a any cruise line.